The prior art has disclosed a host of methods for producing multicoat color and/or effect paint systems. Known from the prior art (cf., e.g., German patent application DE 199 48 004 A1, page 17, line 37, to page 19, line 22, or German patent DE 100 43 405 C1, column 3, paragraph [0018], and column 8, paragraph [0052], to column 9, paragraph [0057], in conjunction with column 6, paragraph [0039], to column 8, paragraph [0050]) is the following method, which involves                (1) applying a pigmented aqueous basecoat material to a substrate,        (2) forming a polymer film from the coating material applied in stage (1),        (3) applying a clearcoat material to the resulting basecoat film, and subsequently        (4) curing the basecoat film together with the clearcoat film.        
This method is widely practiced, for example, both for the original (OEM) finishing of motor vehicles, and for the painting of metal and plastic parts for installation in or on vehicles. In the course of these operations, under certain conditions, adhesion problems occur, particularly between basecoat and clearcoat. Furthermore, the method is also used for the refinishing of motor vehicle bodies. This is a reference not only to OEM motor vehicle refinishing, but also to the motor vehicle refinishing which takes place, for example, in a workshop. A particular problem here is the adhesion between the original finish and the basecoat that is used for refinishing.
It was an object of the present invention, therefore, to provide a polymer which can be used to produce coatings which do not have the above-identified disadvantages of the prior art. This relates to an improvement in adhesion both in the painting of metallic and plastics substrates and in automotive refinish. An important factor in the painting of metallic and plastics substrates, as well as the adhesion of the basecoat to the substrate, is the adhesion between basecoat and clearcoat. In the case of automotive refinish, an important factor, alongside the adhesion between basecoat and clearcoat, is the adhesion between basecoat and original finish. This is to be improved especially for use in OEM automotive refinish.
The problems with adhesion are especially marked when the coated substrates are exposed to weathering. The object of the present invention was therefore also to provide coatings which still possess outstanding adhesion properties even after having been exposed to weathering.
In the case of exposure by weathering, poor adhesion is also manifested in particular in an incidence of blisters and swelling. A further object of the present invention, furthermore, was to prevent or reduce the incidence of blisters and swelling.